Currently available hearing instruments use digital wireless transmission such as radio frequency (RF) not only for remotely controlling the operating parameters for example, volume of the hearing aids (HA) from a handheld unit but also for streaming audio data from a source such as a television, telephone, etc. to the HA, bypassing the acoustic path of a loudspeaker and a microphone and thus eliminating the influence of environmental noise on the perceived audio quality.
High-end hearing instruments generally involve three kinds of devices, that is right and left hearing aids (HA), an audio streamer (AS) and a remote control (RC), which are connected by wireless links. The audio streamer is connected with a stereo audio source and transmits encoded and typically compressed digital audio data to the hearing aids. The hearing aids have two working modes, that is, non-streaming mode and streaming mode. In the non-streaming mode the hearing aids work in a conventional way which is amplifying the acoustic signals picked up by the built-in microphones, while in the streaming mode the hearing aids receive and play back the audio signals transmitted by the audio streamer. The remote control is used to control the functions of the hearing aids, such as volume adjustment, mode switching and so on.
Audio streaming for hearing aids currently exists in at least two varieties, namely direct streaming from the streaming device to the hearing aids, and indirect streaming, in which the audio is streamed to from the streamer to the remote control first and then forwarded, usually using a different wireless technology, from the remote control to the hearing aids.
The devices (HA left/right, AS, RC) must be organized as a system and synchronize in some way so that they can communicate with each other in a robust, reliable and energy-efficient manner, taking into account also the real-time requirements of the streamed audio data. Therefore a flexible and adaptive self-organized systemization mechanism becomes a critical issue.
Hearing instruments form a master-slave configuration over the wireless network, wherein one of the devices such as the left and right hearing aids, the audio streamer and the remote control acts as a master and the rest of the devices act as slave. In this configuration the timing of the channel access by all the slave devices is dependent on the timing of the master.
Currently, in the master-slave configuration one of the devices is configured as a master beforehand and the rest of the devices as slaves which follow the master's timing.
However, in the above-mentioned configuration several problems may arise when the master device doesn't work properly or when the communication between the master and the slave devices is interrupted.